The ship wherein Theseus and the youth of Athens returned had thirty oars, and was preserved by the Athenians down even to the time of Demetrius Phalereus, for they took away the old planks as they decayed, putting in new and stronger timber in their place, insomuch that this ship became a standing example among the philosophers, for the logical question of things that grow; one side holding that the ship remained the same, and the other contending that it was not the same. -- Plutarch

Doesn't this come down to the issue of Interfaces and BlackBox? The interface between the woodsman and the tree is still an ax, which has the same general set of properties: A handle with a length and a head with one or two blades, either of which may have a particular sharpness. -- Wyatt Matthews